In this research, gas-oil gravity drainage (GOGD) mechanism for naturally fractured reservoir is investigated using analytical and numerical approaches. For numerical approach, CMG-GEM commercial software and it newly implemented GOGD functionalities is used. The models of fractured reservoirs, without barrier, with one barrier and two barriers, are created in BUILDER and simulated in GEM (compositional model). It is found that the results of simulations are consistent with the analytical results for immiscible gas injection. The effect of gas type on the oil recovery was investigated by injecting methane and carbon dioxide. Although, immiscible conditions are considered, because of solubility of CO¬2 in oil, injection of CO2 leads to more oil recovery (5% in our example) and gas breakthrough occurs later.